This invention relates generally to the alignment and fixation of bone segments as required for appropriate bone healing, for example after fracture or surgical intervention, and specifically to a device, and the tools needed to install the said device, for the alignment and fixation of cranial bone fragments.
In cases of bone fragmentation where bone fixation is desired, the appropriate alignment of the bone is also a desired result. This is especially true in the cranium, where bone fragmentation can occur as a result of trauma, congenital deformity, or of surgical intervention. In the field of neurosurgery, cranial bone fragments are frequently cut and removed to create defects to allow for access into the cranial cavity and the brain.
The bony cranium is generally regarded to have two surfaces: the outer surface which is characterized by the outer cortex of the bone and is adjacent to the scalp and soft tissue; and the inner surface which is characterized by the inner cortex of the bone and which is adjacent to the cranial cavity and the brain. Between the inner cortex and the outer cortex, which are dense layers of bone, lies the diploe which generally consists of soft bone and bone marrow. When a bone fragment is created, a cut between the bone fragment (the primary bone zone) and the remainder of the cranium (the secondary bone zone) is present.
Several methods of alignment and fixation of primary and secondary bone zones are known. Traditional techniques involve the use of several pieces of filament, such as wire, that are tied after being threaded through holes drilled obliquely through the outer cortex to the cut surface of both bone zones. Precise alignment of the two zones can be difficult and the technique can be cumbersome.
Commonly, the zones of bone can be aligned and fixated with a system of plates and screws (U.S. Pat. Nos. 5,372,598; 5,413,577; and 5,578,036). A plate made of metal or other substance can be fixated to the outer cortex of the primary bone zone with screws whose penetration of the bone can be limited to the outer cortex. With three or more plates attached to the primary bone in such a way that the plates protrude beyond the edges of the primary bone zone, the primary bone zone can be introduced into a defect and aligned to the outer cortex of the secondary bone zone without danger of the primary bone zone falling too deeply into the defect in the secondary bone zone and exerting pressure on the underlying tissue such as the brain. Fixation can then be achieved by employing additional screws fixating the plates to the outer cortex of the secondary bone zone. Plates and screws systems allow for the alignment and fixation of the zones, while preventing the primary bone zone from falling below the level of the secondary bone zone without actually introducing a component of the device below the secondary bone zone. A plate with a spring clip extension has been described (U.S. Pat. No. 5,916,217). Plate and screw systems can be expensive and time consuming to use.
Devices that align the two bone zones by way of compressing them between the two disks positioned along the inner and outer cortex have been described. (Foreign Patents: DE 19603887C2, DE 19634699C1, DE 29812988U1, EP 0787466A1.) A pin connects the two disks aligning and securing two bone zones. These devices introduce foreign material that is left below the inner cortex, and they do not protect the underlying tissue from compression during the installation procedure.
Devices that fixate bone zones using friction forces created by a cam without a component that extends below the inner cortex are known and described (Patent DE 19634697C1). These devices also do not protect the brain from compression during the installation procedure.
Intramedulary pins are well known in the orthopedic fields for alignment of long bones. Such pins have also been described for cranial fixation (U.S. Pat. No. 5,501,685); however, the bone zones can not be aligned in three dimensions with this technique.
There is a need for an alignment and fixation device that is simple and rapid to use, versatile, and ultimately cost effective.